Point-of-Care (POC) testing systems and fluidic devices or cartridges are becoming more common because of the advancement in microfabrication technology such as MEMS technology, which enables the fabrication of reliable and inexpensive fluidic based cartridges. Generally, such systems use microvalves, micropumps, microneedles, etc. for moving the fluids through the fluidic system. A common system contains a reagent reservoir, a mixing chamber, an analytical chamber and waste chamber. Fluids must therefore be moved from one chamber to another. Some challenges in moving such fluids in a fluidic device include mixing the reagents with the sample, and washing unbound reagents from a detection site. One of the common challenges is washing the unbound conjugates after the incubation period, particularly removing conjugates that remain stuck to the edges of the reaction site walls. U.S. Pat. No. 5,600,993 provides a good summary of such exemplary problems.
Various approaches that have been described to cause fluid movement in a fluidic device include electrical, osmotic, and capillary. U.S. Pat. No. 6,440,725 describes different fluid motive sources for moving liquids through the chambers. One such example uses a fluid inside a sealed pouch wherein the fluid is converted to gas by an electrical current. This action pressurizes and expands the fluid pouch. This sealed pumping pouch, or e-pump, is positioned against a reagent pouch and forces the contents of the reagent pouch into the fluidic circuit as the pumping pouch expands. The '725 patent also describes various other fluid motive sources such as pressure or vacuum source, or using a solenoid or stepper motor to provide a force to press against a reagent pouch.
US Patent Application No. 20050130292 describes using mechanical energy to move fluids within a fluidic device. In this application the inventors describe minimal or no external power to force the fluid through various chambers. A sample is loaded on to a biochip and this biochip is inserted into a custom designed socket. The work done in inserting the socket is converted to the energy required for the fluidic flow. Subsequent steps of directing the sample to the desired chamber, mixing it, and assaying it are, according to the inventors, accomplished with minimal power consumption. Such a device has several valves and pumps, even if the pumps are not driven by external electrical energy, which are difficult to include in a small disposable fluidic system.
Generally, reagents in a POC system are stored in a dry state to improve shelf-like. Buffers are generally stored separately until the assay is to be performed, at which time the reagents are hydrated. However, dry reagents may become wet or hydrated before they are intended to do so. Buffers may leak from their holding areas and mix with the dry reagents. It may thus be beneficial to keep the dry reagents in a dry state until the assay is initiated.
Cartridge or fluidic based POC systems may handle small volumes of fluids. Nanoliter or even picoliter amounts of fluids are sometimes forced to flow within fluidic channels. Either during the sample introduction or a venting process, there is a substantial likelihood that a bubble will be introduced into the microfluidics system. A bubble introduced into the system can cause an inaccurate measurement if the bubble is located in the detection site during the detection step.
Current fluidic devices may experience optical cross-talk when there are multiple reaction sites adjacent to one another. When assays with different luminescent intensities are run in adjacent reaction wells or chambers, photons (representing the signal generated) can travel from one well to others comprising the accuracy of measurement from each well. The photons can travel through construction materials of the wells and through the fluidic channels that connect the wells. This problem may become worse the longer the incubation time of the assay. Thus, there remains a considerable need for new designs of fluidic cartridges with reduced optical interference from adjacent reaction sites. The present invention satisfies this need and provides related advantages as well.